The present invention relates to an air blast type slag cut off device for steel converter, adapted to force back, by an application of a high-pressure gas such as pressurized air, pressurized nitrogen and so forth, the slags which tend to come out of the tap hole of the converter together with the molten steel, thereby to prevent the slag from being discharged from the steel converter.
More particularly, the invention is concerned with an improvement in the air blast type slag cut off device, in which the time lag or delay of the actual starting of the air blast after the opening of the shut-off valve for the pressurized gas.